Project Summary The communication impairments associated with aphasia limit participation in vocational and other activities, such as socializing with family or friends and medical decisions. The resulting social isolation is often a long-term issue due to the chronic nature of aphasia and limited access to speech language services. The goal of this research is to answer a relatively basic question about how to format treatment for people with aphasia: How many people should be in treatment sessions? Group treatment has the potential to improve communication and reduce social isolation, while also reducing medical costs. However, this treatment format lacks a strong evidence base. This project seeks to address this problem by investigating how two conflicting hypotheses ? treatment dosage and group dynamics ? affect conversational treatment outcomes. Treatment dosage refers to the idea that treatment benefits are enhanced when clients have a greater number of practice trials during treatment. This hypothesis predicts that clients will show greater treatment effects when treatment sessions involve a small number of clients, because clients have many opportunities to practice target skills. Group dynamics refers to the hypothesis that working with a group of peers who have similar impairments leads to better treatment outcomes than working with smaller groups of clients, due to variables such as interpersonal learning. The proposed study will compare these hypotheses in the context of a well-motivated and operationalized conversational treatment. Across two sites, we will enroll 48 participants with chronic aphasia due to a stroke in the language-dominant hemisphere. All participants will be randomly assigned to one of three conditions: dyad treatment (2 clients per session), traditional group treatment (8 clients per session) or delayed control group. Treatment will occur for 60 minutes, twice a week for 10 weeks. During treatment sessions, a speech pathologist will facilitate discourse using linguistic and multimodal cueing hierarchies, which will be tailored to individual client goals. The primary outcome measure will evaluate how efficiently individuals with aphasia communicate information during a picture description task. Additional outcome measures will include standardized tests and patient reported outcome measures, which evaluate both changes in real-world communication ability and in social isolation. We will examine treatment effects associated with dyads and traditional groups immediately after treatment and one year after treatment, in order to determine whether treatment effects persist over time. This is a significant contribution because it will advance knowledge regarding how to optimize treatment for individuals with chronic aphasia. This study also provides the foundation for a research program that will systematically examine conversational treatment, including how differences in the treatment and individual (e.g., aphasia severity) influence treatment outcomes.